Back when the NHL was actually playing, does anyone know how the Islanders got to their away games and what airport they flew out of? I know the Red Wings have their own DC9 but is this the case for most NHL teams?

They have used not only the YX DC9-30, but also MD-81 equipment from FRG. I think the size of the aircraft used just usually depends on what YX has on hand (unless the length of the flight necessitates using an MD-81), I've seen them use M81 to BOS, but also use D93 to FLL. On flights to the west coast, they usually fly an MD-81 and refuel at MCI.